There are no cable cars running between Interlaken and Murren. The cable cars are between Lauterbrunnen and Grutschalp (with a change to a cog train to Murren) and between Gimmelwald to Murren. If you helicopter into the Schilthorn, you can take the cable car down to Murren.
There are alternate ways to get to Murren by cable car (gondola). If one is down for maintenance, you can take the alternate method. If any are down for maintenance, www.rail.ch will not permit the trip to be booked on the down system. They will book you on the alternate.
Note that it will be "shoulder season" in Murren in mid-April. This is the dowtime necessary to change from ski season to summer tourist season. Most places in the alpine villages are closed. Check with your hotel. Some do stay open but it's quiet up there.